nameSpan is incorrect for backquoted names with escaped characters

[TheElectronWill]

Compiler version

3.2.1-RC2

Minimized code

def `\r\n`() = ()

Output

val methodDef: DefDef = ... // get the DefDef of the method
val namePos = methodDef.namePos
println(namePos.span)

[45..47] // the span is only 2 chars long

The span is wrong because Trees#nameSpan computes the span's end from realName.length, but since the characters were escaped the count is wrong.

This is annoying for coverage reports, where namePos is used to "highlight" the method name in the coverage report.

Expectation

The correct span should match the original source, thus it should be [45..49] (not sure whether the quotes should be included or not).
The Parser produces an Ident with the correct span (here, I think), could this be used instead?

[odersky]

The problem is that doing this would grow significantly the size of all trees, lowering performance, whereas the use case where this matters is very marginal. If we can come up with a scheme that does not increase the size of definition nodes, fine. Otherwise it should be a won't fix.

[TheElectronWill]

Mitigation idea: when computing the namePos, escape the characters of the name if needed. In the example I gave, we know that the name must have been written `\r\n` because CRLF isn't a valid name without backticks and escapement.

Speaking of backticks, the REPL could automatically add backticks and escapes where needed, to avoid this:

that would be another issue, but the two might be related because the automatic backticking+escaping would be the same.

[dwijnand]

Mitigation idea: when computing the namePos, escape the characters of the name if needed.

That doesn't help def `foo` = 1, which doesn't need backticks, but is still 5 characters long rather than 3.

[TheElectronWill]

That doesn't help def `foo` = 1, which doesn't need backticks, but is still 5 characters long rather than 3.

Without having a "backticked" flag there's not much we can do then 🤔 I've thought about making the name start at ` instead of f, and then detecting the backtick, but removing the backtick everytime we use the name is too heavy.